i. Field of the Invention
This invention is concerned with equipment and techniques for transferring heat to or from material within a vessel or container and in particular, seeks to provide means whereby mechanical stresses in such vessels can be greatly reduced to allow for extremes of physical dimensions, temperature, and other operational stresses such as corrosive atmosphere.
II. Description of the Prior Art
While the use of fluidised beds to transfer heat to the surfaces of a kinetic heat exchanger located within the bed is well known in the art, all such arrangements employ fluid in the heat exchanger and are therefore not suitable for the indirect drying or freezing of particulate solids by passage of the particulate solids through the heat exchanger.
On the other hand, while indirectly heated fixed retorts with either static or moving charges are also well known, as for example coal gasification retorts or zinc volatilisation retorts, the need to use complex mechanical means to effect solids movement therein and therefrom restricts their use.
A further disadvantage is the inefficient rate of heat transfer to and from the static or relatively immobile contents of such retorts. Directly or indirectly heated rabbled furnaces are also known, but the need to stir or rake the contents presents considerable technical problems especially where high temperatures and corrosive atmospheres are involved. Similarly, although rotating kilns and freezing tunnels provide a well-known means of agitating the substance to effect efficient heat transfer, the problems associated with gaseous direct heating or cooling are inherent. Moreover, the mechanical difficulties of operating large kilns of this nature at high temperatures in a corrosive atmosphere are frequently critical.
An object of the invention is to provide techniques which combine many of the advantages of the above prior art systems while at least partly avoiding the disadvantages thereof.